1. Field of the Invention
The present invention relates to a liquid crystal display and a method of producing the same, in particular, to a liquid crystal display in which a reflective type display and a transmissive type display are used together, and a normally black mode is adopted, and a method of producing the same.
2. Description of the Related Art
A liquid crystal display has an advantage of thin shape, lightweight, low power consumption in comparison with a CRT (Cathode Ray Tube) display, therefore it is used as display devices for various electronic devices, such as a personal computer, a cellular phone, a digital camera.
The liquid crystal display is classified roughly to a transmissive type and a reflective type. The liquid crystal display is, different from the CRT display, not a self-luminous display. Consequently, the transmissive type liquid crystal display has a flat surface light source as the light source in the reverse surface, called as a backlight. Displaying is performed by the light from a backlight transmitted a liquid crystal panel. The transmissive type liquid crystal display has advantages of being unaffected in the case that surrounding light is weak and being possible to displaying in high luminance and high contrast, since displaying is performed by using a backlight.
However, since the backlight accounts for more than 50 percent of all electric power consumption of the liquid crystal display, the transmissive type liquid crystal display has a problem that it is difficult to decrease the electric power consumption. Moreover, in the case that surrounding light is strong, there is some problems that displaying looks darkly, and visibility gets worse.
On the other hand, the reflective type liquid crystal display, surrounding light is used as a light source, the surrounding light source is reflected by a light reflector, the display is performed when the reflected light is transmitted a liquid crystal panel. Since, it is necessary to convert the surrounding light that is a point light source into a surface illuminant on the display surface, the light reflector has an uneven surface for diffuse-reflection. The reflective liquid crystal display like this has an advantage of low electric power consumption, because the reflective type liquid crystal display that is different from the transmissive type liquid crystal display does not use a backlight. However, when the surround is dark, since a reflected light is small, luminance and contrast is not enough and visibility gets worse. In particular, in the case of color display, usability of the reflected light goes down by the color filter and visibility gets especially worse.
To overcome the disadvantage, in the transmissive and the reflective type liquid crystal display, for example, Japanese unexamined patent publication No. 2001-318377 discloses that the semi-transparent or the combination type liquid crystal display, that the transmissive type display and the reflective type display is used together. The combination type liquid crystal display displays by applying reflection of the surrounding light when the surround is light, by applying a backlight when the surround is dark.
FIG. 10 is a plan view of one pixel of the existing combination type liquid crystal display. FIG. 11 is a perspective view of one pixel of the existing combination type liquid crystal display.
As shown in FIG. 10, the combination type liquid crystal display has in one pixel the both of the reflective region Ar10 that the reflective electrode is formed, and the transmissive region Ar20 that the transparent electrode is formed. As shown in FIG. 11, the liquid crystal layer 130 is wedged between the first substrate 110 and the second substrate 120. On the first substrate 110 side, an unevenness reflective electrode is formed in the reflective region Ar10, and a transparent electrode is formed in the transmissive region Ar20.
The first substrate 110 is a so-called TFT (Thin Film Transistor) substrate, a switching element that is formed with TFT etc., an auxiliary capacitance line, a gate line and a signal line are formed. As well, in FIG. 11, for simplification of a figure, a signal line 112 is only shown.
In the case of the combination type liquid crystal display, in the reflective region Ar10, since the light passing through the liquid crystal layer 130 is reflected by the reflective electrode, and passes through the liquid crystal layer 130 again, the light passes through the liquid crystal layer 130 twice in all. However, in the transmissive region Ar20, the transmitted light passes through the liquid crystal layer 130 only once. Therefore, it is necessary that the thickness of the liquid crystal layer 130 in the transmissive layer Ar20 is designed to be the twice thickness of the liquid crystal layer 130 in the reflective region Ar10.
On the other hand, there is many normally white mode liquid crystal display that transmittance of the transmissive region becomes the maximum in voltage non-applied condition as the combination type liquid crystal display. This is, generally, why by adopting normally black mode, that the transmittance of the transmissive region becomes the minimum in voltage non-applied condition, the good “black” display is difficult in voltage non-applied condition.
However, in the combination type liquid crystal display of normally white mode, it is necessary to establish on one side of a liquid crystal panel, on the other side of the panel two optical retardation films and one polarizer. In fact, it is necessary to locate six sheets in all on both sides. On the other hand, in normally black mode, on one side of a liquid crystal panel one optical retardation film and one polarizer on the other side of the panel, one polarizer or one polarizer and one optical retardation film should be located, there is an advantage that the number of parts decreases.
However, in normally black mode, since the cell gap between the reflective region Ar10 and the transmissive region Ar20 is adjusted by a layer 111 formed below a reflective electrode of the first substrate 110, there is a step C on the boundary of the reflective region Ar10 and the transmissive region Ar20 on the first substrate 110.
By existing the step C for adjusting the thickness of the liquid crystal layer 130 on the boundary of the reflective region Ar10 and the transmissive region Ar20 on the first substrate 110, the alignment of the retardation of this part is inadequate, and as shown in FIG. 12, there is a problem that the light leakage region Ar30 is generated. Thereby, at the transmissive region Ar20 that high contrast is needed especially, there is a problem that enough contrast is unavailable.